This invention concerns a calender, especially a soft calender including a body structure and at least two roller sets, wherein there is at least one calendering nip formed in between two rollers, and of the rollers forming the nip at least one is a roller with a soft surface and the other roller is a heating roller.
As is known in the state of the art, in the after-treatment of fibre webs, especially paper and board webs, calenders are used in order to increase the smoothness and evenness of the web surface. Of the rollers forming the calender nip in the soft calender, at least one of the rollers forming the nip has a soft surface. The soft calender nip is usually formed by at least one variable crown roller having a soft surface coating and by a heating chill roller. Multi-zone roller technology known as such is used for the thickness calibration of the web. In soft calendering, the mechanism affecting the web surface consists of compression and copying. High temperatures can be utilised in soft calendering, and this is mainly applied with such grades, which were earlier calendered by machine-finishing, and it is suitable e.g. for calendering of newsprint and fine grade papers as well as various kinds of board. Single-nip and double-nip as well as multi-nip soft calenders of many different types are known in the state of the art.
One known soft calender is presented in the FI Patent Publication 74066, which describes an arrangement, wherein the web consisting of paper or other such material is subjected to the effect of at least one nip, which nip is formed by an iron roller and a flexible roller. The iron roller is heated at least to such a temperature, at which the shape of fibres begins to change. With paper this is approximately (177° C.) 350° F. The web is preferably run between two nips, whereby the first nip will polish one side of the web while the other nip will polish the other side. In this way a minimum-stippled web is obtained having improved gloss without any loss of bulk.
Another known soft calender, especially an arrangement and adaptation for fastening a calender roller, is presented in the FI Application Publication 992214, in which known calender there are at least two calender nips formed by at least two superimposed rollers, bearing housings used for combining the rollers to form roller pairs forming calender nips and parts for fastening together the bearing housings of the roller pairs. In this known calender at least two successive calender nips are arranged in such a way that the distance between the center lines of the lower rollers in the successive nips is shorter than the distance between the center lines of the rollers located above them, whereby as seen from the roller end faces the rollers are in a V position and a space is formed between the nips for replacement of the rollers.
Nowadays when using calenders, especially soft calenders, as an on-line after treatment device in lines for making paper or board webs, one important factor is the time used for exchanging the rollers. The time used for exchanging the rollers reduces the production capacity, and for this reason it is important to minimise the time spent for exchanging rollers in the calender. It is of course important also with off-line calenders to minimise the time spent for exchanging the rollers.
The invention aims at bringing about a calender, where the rollers are exchanged quickly.
Nowadays calendering of different types is also needed to make different paper grades, whereby versatility of the calender is an important feature.
The invention also aims at bringing about a calender, which is easily converted.